Centrifugal pump assembly for use in nuclear reactor plants or the like

ABSTRACT

A vertical centrifugal pump assembly for use as a primary recirculating pump in a nuclear reactor plant has an uppermost shaft which is driven by a motor, a lowermost shaft which drives the impeller of the pump, and an intermediate shaft which is movable axially between the uppermost and lowermost shafts and carries a housing for radial and/or thrust bearings. A rigid coupling between the lowermost shaft and the intermediate shaft is disengaged when the intermediate shaft is lifted to thereby afford access to certain parts of the lowermost shaft. The uppermost shaft can drive the intermediate shaft through the medium of a flexible coupling having coupling elements mounted on the lower end of the uppermost shaft and the upper end of the intermediate shaft, and a distancing sleeve whose internal threads are in permanent mesh with external threads of the two coupling elements. A shroud which surrounds the flexible coupling has a maximum-diameter tubular section rigid with the housing for the bearings, a minimum-diameter tubular section rigid with but detachable from the casing of the motor, and a median tubular section which penetrates into the maximum-diameter section when the intermediate shaft is lifted. When the minimum-diameter section is detached from the casing of the motor, it can be slid, together with the intermediate section, into the maximum-diameter section to thereby afford access to the flexible coupling. The rigid coupling has two coaxial coupling elements which are mounted at the upper end of the pump shaft and the lower end of the intermediate shaft and may have teeth which mate when the intermediate shaft assumes its lower end position in which it can drive the pump.

United States Patent 1191 Honold et al.

[ NOV. 11, 1975 CENTRIFUGAL PUMP ASSEMBLY FOR USE [57] ABSTRACT IN NUCLEAR REACTOR PLANTS OR THE A vertical centrifugal pump assembly for use as a pri- LIKE mary recirculating pump in a nuclear reactor plant has [75] Inventors: Ernst Honold; Michael Riipp, both an uppermost which dnYen by a motor a of Frankenthal Germany ermost shaft WhlCh drives the impeller of the pump, t j and an intermediate shaft which is movable axially be- Asslgneel in, Schan ln Becker tween the uppermost and lowermost shafts and carries Aktlellgesellschaft,Ffaflkenthal, a housing for radial and/or thrust bearings. A rigid Germany coupling between the lowermost shaft and the inter- [22] Filed; 12, 1973 mediate shaft is disengaged when the intermediate shaft is lifted to thereby afford access to certain parts PP 426,629 of the lowermost shaft. The uppermost shaft can drive the intermediate shaft through the medium of a flexi- [30] Foreign Application priority Data ble coupling having coupling elements mounted on the D l 6 1972 G 2261643 lower end of the uppermost shaft and the upper end of the intermediate shaft, and a distancing sleeve whose internal threads are in permanent mesh with external [52] Cl threads of the two coupling elements. A shroud which [51] Int Cl 1516! 3/06 surrounds the flexible coupling has a maximum- 58] Fieid 1 C l R diameter tubular section rigid with the housing for the 64/ S J bearings, a minimum-diameter tubular section rigid 5 with but detachable from the casing of the motor, and a median tubular section which penetrates into the 56] R f Cted maximum-diameter section when the intermediate e emces shaft is lifted. When the minimum-diameter section is UNITED STATES PATENTS detached from the casing of the motor, it can be slid, 521,677 6/1884 Smith 64/1 C together with the intermediate section, into the max- 2,830,801 4/1 58 Stratico o et 403/286 imum-diameter section to thereby afford access to the 2,959,943 11/1960 Allen 69/9 fl ibl coupling The rigid coupling has two coaxial 3 32; E

23 3; coupling elements which are mounted at the upper 32323 3:22 at a 5/1/22 end of the pump shaft and the lower end of the intermediate shaft and may have teeth which mate when Primary Emminer samuel Scott the intermediate shaft assumes its lower end position Assistant ExaminerRandall Heald m whlch It can dnve the pump Attorney, Agent, or FirmMichael S. Striker 12 Claims 3 Drawing Figures 1 in. E= in,

l j l i g I l A 6 I 1 2a.

US. Patent Nov.11, 1975 Sheet2of3 3,918,272

U.S. Patent Nov. 11, 1975 Sheet 3 of3 3,918,272

CENTRIFUGAL PUMP ASSEMBLY FOR USE IN NUCLEAR REACTOR PLANTS OR THE LIKE BACKGROUND OF THE INVENTION The present invention relates to improvements in centrifugal pump assemblies in general, and more particularly to improvements in upright pump assemblies of the type which may constitute the primary recirculating pumps for use in nuclear reactor plants, for example, in pressurized water reactors.

It is already known to provide a primary recirculating pump with three coaxial shafts including a lower shaft or pump shaft, an intermediate shaft for the necessary radial and/or thrust bearings, and an upper shaft or motor shaft which is driven by the prime mover. The torque-transmitting connection between the pump shaft and the intermediate shaft constitutes a rigid coupling, and the torque-transmitting connection between the intermediate shaft and the motor shaft constitutes a flexible coupling. In such primary recirculating pumps, it is customary to separably connect a first unit including the pump, the seal for the pump shaft and the bearing for the pump shaft with a second unit including the bearing housing, thrust bearing and the upper radial bearing. This is advisable in view of the fact that the pump assembly is mounted in vertical position. The second unit including the bearing housing, the thrust bearing and the upper radial bearing is installed in a supporting bellows and is connected with the prime mover by the aforementioned flexible coupling. The coupling between the first unit and the second unit is rigid. A relatively long removable liner or envelope is provided to allow for rapid installation or removal of the antifriction bearing for the pump shaft and/or shaft seal without interrrupting the connection between the bearing housing and the prime mover. The just mentioned liner contributes to the overall length of the assembly including the three shafts. Moreover, the upper and lower ends of the removable liner must be installed in the aggregate by resorting to two discrete auxiliary couplings which contribute to the initial and maintenance cost and whose engagement or disengagement takes up substantial amounts of time.

SUMMARY OF THE INVENTION An object of the invention is to provide a novel and improved vertical pump assembly which is'more rigid, shorter and less complex than heretofore known pump assemblies, and wherein the parts which require frequent inspection, repair and/or replacement can be reached with little loss in time.

Another object of the invention is to provide a pump assembly which can dispense with the aforediscussed liner and auxiliary couplings and wherein the intermediate shaft is connected with the output shaft of the prime mover in a novel and improved way.

A further object of the invention is to provide an improved primary recirculating pump assembly for use in nuclear reactor plants.

An additional object of the invention is to provide a novel shroud between the prime mover and the intermediate shaft of the improved pump assembly.

The invention is embodied in a centrifugal pump assembly, particularly in a primary recirculating pump for use in nuclear reactor plants. The pump assembly comprises an upright motor shaft, a pump shaft which is coaxial with and is spaced apart from the motor shaft,

a bearings-carrying intermediate shaft which is coaxial with, disposed between and movable axially relative to the other two shafts between an operative position in which it can drive the pump shaft and an inoperative position, a first coupling (preferably a flexible coupling) which is provided between the motor shaft and the intermediate shaft, and a second coupling (preferably a rigid coupling) which is provided between the intermediate shaft and the pump shaft. One of the cou plings (preferably the second coupling) is disengaged in automatic response to movement of the intermediate shaft from its operative position. The motor shaft is normally disposed above the intermediate shaft.

The flexible coupling preferably includes a first externally toothed coupling element rigid with the motor shaft, a second externally toothed coupling element rigid with the intermediate shaft, and a distancing sleeve preferably having two discrete sets of internal teeth in permanent mesh with the external teeth of the two coupling elements.

In accordance with another feature of the invention, the flexible coupling is normally surrounded by a variable-length shroud which has a maximum-diameter tubular section secured to the housing for bearings on the intermediate shaft, a minimum-diameter section separably secured to the casing of the prime mover which drives the motor shaft, and a median section which is telescoped into the maximum-diameter section and telescopically receives the minimum-diameter section. When the intermediate shaft is moved to its inoperative position, the maximum-diameter section moves with the intermediate shaft whereby at least the median section penetrates into the maximum-diameter section. When the attendants wish to gain access to the flexible bearing in operative position of the intermediate shaft, the minimum-diameter section is detached from the casing of the prime mover and is moved, together with the median section, into the interior of the maximumdiameter section.

The coupling between the pump shaft and the intermediate shaft may include two coaxial coupling elements having radially extending complementary teeth which mate in the operative position of the intermediate shaft.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved pump assembly itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary axial sectional view of a pump assembly which embodies one form of the invention, the intermediate shaft being shown in its operative position;

FIG. 2 illustrates the structure of FIG. 1 but with the intermediate shaft in raised or inoperative position; and

FIG. 3 is a partly elevational and partly axial sectional view of a modified rigid coupling between the pump shaft and the intermediate shaft.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the novel parts of the pump assembly in 4 mover. The shroud is then collapsed by respectively pushing its sections 5, 5 downwardly into the sections 5, 5" so that the overall axial length of the shroud is reduced to equal or closely approximate the axial ln pump assemblies to which the present invention pertains, it is normally desirable to leave the prime mover in fully assembled condition when the parts which are mounted on the shaft la and/or 2 require attention. Moveover, the torque-transmitting connection between the prime mover and the pump should be as short as possible without, however, preventing access to parts on the shaft la and/or 2. Such parts include primarily the shaft seals, the bearing or bearings for the pump shaft, and the axial and/or radial bearings (in the housing 1) for the output shaft 8a of the prime mover. All this is achieved by the aforedescribed construction of the improved pump assembly with the additional advantage that the distance between the bearings for the shafts 8a, 2 is less than in conventional pump assemblies which contributes to rigidity and longer useful life of the apparatus.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution of the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. In a centrifugal pump assembly, particularly in a primary recirculating pump for use in nuclear reactor plants, a combination comprising an upright motor shaft; a pump shaft coaxial with and spaced apart from said motor shaft; a bearings-carrying intermediate shaft coaxial with, disposed between-and movable axially relative to said first mentioned shafts between an operative position and an inoperative position; a first coupling provided between said motor shaft and said intermediate shaft; a variable-length shroud normally surrounding said first coupling; and a second coupling provided between said pump shaft and said intermediate shaft, one of said couplings being respectively engaged and disengaged in said operative and inoperative positions of said intermediate shaft.

2. A combination as defined in claim 1, wherein said motor shaft is disposed above said intermediate shaft.

3. A combination as defined in claim 2, wherein said one coupling is a rigid coupling and constitutes said second coupling.

4. A combination as defined in claim 3, wherein said second coupling comprises a first coupling element rigid with said pump shaft and a second coupling element rigid with said intermediate shaft and engaging 6 said first coupling element only in said operative position of said intermediate shaft.

5. A combination as defined in claim 1, wherein said first coupling is a flexible coupling and includes a sleeve-like first coupling element receiving torque from said motor shaft, a second coupling element provided on and movable axially with said intermediate shaft, and means for maintaining said second coupling element in torque-receiving engagement with said first coupling element in all axial positions of said intermediate shaft.

6. A combination as defined in claim 1, wherein said shroud comprises a plurality of telescopically connected tubular sections including a first section mov-' able with said intermediate shaft, a second section normally connected with said motor shaft and a median section.

7. A combination as defined in claim 6, wherein the diameter of said first section exceeds the diameters of the other sections of said shroud sothat at least one of said other sections enters said first section in response to movement of said intermediate shaft to said inoperative position.

8. A combination as defined in claim 7, wherein said second section of said shroud is separable from said motor shaft and is thereupon movable with said median section into said first section to thereby at least partially expose said first coupling.

9. A combination as defined in claim 1, wherein said first coupling is a flexible coupling and comprises a first coupling element rigid with said motor shaft, a second coupling element rigid with said intermediate shaft, and a distancing sleeve arranged to transmit torque from said first to said second coupling element.

10. A combination as defined in claim 9, wherein said first and second coupling elements have external teeth and said sleeve has internal teeth mating with said external teeth of said coupling elements in each axial position.of said intermediate shaft.

11. A combination as defined in claim 10, wherein said internal teeth include discrete first and second sets of teeth which respectively mate with the external teeth of said first and second coupling elements.

12. A combination as defined] in claim 1, wherein said one coupling is said second coupling and said second coupling comprises coaxial first and second coupling elements respectively rigid with said pump shaft and said intermediate shaft, said coupling elements having complementary teeth which mate in said operative position of said intermediate shaft. 

1. In a centrifugal pump assembly, particularly in a primary recirculating pump for use in nuclear reactor plants, a combination comprising an upright motor shaft; a pump shaft coaxial with and spaced apart from said motor shaft; a bearingscarrying intermediate shaft coaxial with, disposed between and movable axially relative to said first mentioned shafts between an operative position and an inoperative position; a first coupling provided between said motor shaft and said intermediate shaft; a variable-length shroud normally surrounding said first coupling; and a second coupling provided between said pump shaft and said intermediate shaft, one of said couplings being respectively engaged and disengaged in said operative and inoperative positions of said intermediate shaft.
 2. A combination as defined in claim 1, wherein said motor shaft is disposed above said intermediate shaft.
 3. A combination as defined in claim 2, wherein said one coupling is a rigid coupling and constitutes said second coupling.
 4. A combination as defined in claim 3, wherein said second coupling comprises a first coupling element rigid with said pump shaft and a second coupling element rigid with said intermediate shaft and engaging said first coupling element only in said operative position of said intermediate shaft.
 5. A combination as defined in claim 1, wherein said first coupling is a flexible coupling and includes a sleeve-like first coupling element receiving torque from said motor shaft, a second coupling element provided on and movable axially with said intermediate shaft, and means for maintaining said second coupling element in torque-receiving engagement with said first coupling element in all axial positions of said intermediate shaft.
 6. A combination as defined in claim 1, wherein said shroud comprises a plurality of telescopically connected tubular sections including a first section movable with said intermediate shaft, a second section normally connected with said motor shaft and a median section.
 7. A combination as defined in claim 6, wherein the diameter of said first section exceeds the diameters of the other sections of said shroud so that at least one of said other sections enters said first section in response to movement of said intermediate shaft to said inoperative position.
 8. A combination aS defined in claim 7, wherein said second section of said shroud is separable from said motor shaft and is thereupon movable with said median section into said first section to thereby at least partially expose said first coupling.
 9. A combination as defined in claim 1, wherein said first coupling is a flexible coupling and comprises a first coupling element rigid with said motor shaft, a second coupling element rigid with said intermediate shaft, and a distancing sleeve arranged to transmit torque from said first to said second coupling element.
 10. A combination as defined in claim 9, wherein said first and second coupling elements have external teeth and said sleeve has internal teeth mating with said external teeth of said coupling elements in each axial position of said intermediate shaft.
 11. A combination as defined in claim 10, wherein said internal teeth include discrete first and second sets of teeth which respectively mate with the external teeth of said first and second coupling elements.
 12. A combination as defined in claim 1, wherein said one coupling is said second coupling and said second coupling comprises coaxial first and second coupling elements respectively rigid with said pump shaft and said intermediate shaft, said coupling elements having complementary teeth which mate in said operative position of said intermediate shaft. 